The Synthesis, Characterization, and Reactivity of First-Row Late Transition Metal Complexes Containing Tridentate Pincer-Type N-Heterocyclic Phosphenium Ligands Master’s Thesis Presented to The Faculty of the Graduate School of Arts and Sciences Brandeis University Department of Chemistry Christine M. Thomas, Advisor In Partial Fulfillment of the Requirements for the Degree Master of Science in Chemistry by Sadie E. Knight February 2015 Copyright by Sadie E. Knight © 2015 Acknowledgements I would like to acknowledge Christine Thomas for helping me cultivate a thick skin and for making important life decisions for me. I’d like to thank Bruce Foxman for managing the X-ray structure determination facility and Mark for solving my complex crystal structures. Thank you to Francesco Pontiggia for all the computational help you provided me, especially when I was in a real pinch. A very special thanks goes to Rebecca Menapace for being a true mentor, supporting me, and appreciating the work I do. Thank you for inviting me to join your team of warm and friendly professionals in the OTL. I truly appreciate some of my lab mates and fellow indentured servants, especially my dear friends Deirdra, Jenn and Sölen. I have enjoyed learning and working with Deirdra, Seth, Jeremy, Baofei, Kuppu, Ramyaa, Bing, Katie, Penny and silly Noam. You have all taught me a lot about science, politics, comedy, and other worldly matters. I would like to expressly thank my parents for always supporting me and showering me with love and wisdom. You have taught me to be strong and to think independently. Thanks, Dad, for all your advice on chemistry and office politics. Mama, thank you for bestowing me with the sass and the courage to always stick up for myself. Thank you to my sweet brothers, Tommy and Tristan, for always being there for me. Finally, I would like to thank the love of my life and my best friend, James Dillon, who has never stopped believing in me. You have been my constant throughout this whole experience and taught me how to have confidence in myself as a woman and a scientist. I love you forever and can’t wait for you to join me in the real world. iii ABSTRACT The Synthesis, Characterization, and Reactivity of First-Row Late Transition Metal Complexes Containing Tridentate Pincer-Type N-Heterocyclic Phosphenium Ligands A thesis presented to the Department of Chemistry Graduate School of Arts and Sciences Brandeis University Waltham, Massachusetts By Sadie E. Knight First-row late transition metal complexes featuring N-heterocyclic phosphine- and phosphenium-containing tridentate pincer ligands have been synthesized and their reactivity has been investigated. The coordination chemistry of a diphosphine pincer ligand incorporating an N-heterocyclic phosphenium cation ([PPP]+) and its halophosphine precursors ([PP(X)P] has been explored using cobalt(II), iron(II) and copper(I) reagents. Treatment of CoCl2 with [PP(Cl)P] led to the neutral coordination complex [PP(Cl)P]CoCl2, which led to the fluoride-abstracted species [PP(F)P]CoCl2 upon exposure to AgPF6 instead of forming a phosphenium-cobalt species. This behavior highlights the electrophilic nature + of the [PPP] ligand within a [(PPP)CoCl2][PF6] intermediate. When the [PP(X)P] precursors were treated with copper(I) halides, simple [PP(X)P]CuY coordination compounds formed (X and Y = Cl or I). The iodophosphine- copper complex [PP(I)P]CuI was shown to react with THF, resulting in a ring-opening insertion to form the alkoxyphosphine complex [PP(O-CH2CH2CH2CH2-I]CuI, a behavior iv that was also observed for iron species. Reacting the halide-free phosphenium ligand [PPP][BPh4] with CuCl led to [PP(Ph)P]CuCl, the product of phenyl group abstraction from - [BPh4] by the electrophilic phosphenium-copper intermediate species, [(PPP)CuCl][BPh4]. Arylphosphine products [PP(Mes)P]CuCl and [(PP(Mes)P)-Cu][BArF20] were obtained via transmetallation between starting materials and mesityl migration, respectively. Treatment of CuCl with [PPP][BArF20] led to the dimerization product [(PP(Cl)P- Cu)2][BArF20]. Preliminary density functional theory (DFT) calculations suggest that [(PP(Cl)P-Cu)2][BArF20] resulted from the coupling of cationic chlorophosphine- and phosphenium-copper monomer intermediates. Finally, a new tridentate hemilable mixed-donor ligand containing a central cationic N-heterocyclic phosphenium donor with a rigid phenylene backbone flanked by two ethylenepyridine side arms ([NPN]+) was synthesized. Using DFT methods, it was shown that [NPN]+ was less electrophilic and a weaker π-acceptor than [PPP]+. The coordination chemistry of the phosphenium precursor ([NP(Cl)N]) with a Pd(PPh)3 resulted in a trimetallic NHP-bridged complex [NPN]2Pd3(PPh3)3Cl2, where the pyridyl groups do not take part in any coordination. Structural and theoretical studies suggest an NHP+ phosphenium description for the µ-NHP units, bound to zero valent palladium centers. Formation of diamagnetic species [NP(Cl)N]CuCl occurs upon treatment of CuCl with [NP(Cl)N], while the reaction between [NPN][BArF20] and CuCl yields a paramagnetic I II product, proposed to be either [(NPN)Cu Cl][BArF20] or diradical [(NP N)Cu Cl][BArF20]. v Table of Contents Acknowledgement ............................................................................................................................................................ iii ABSTRACT ...................................................................................................................................................................... iv Table of Contents ............................................................................................................................................................... vi List of Abbreviations and Nomenclature ................................................................................................................ ix Chapter 1. History and development of N-heterocyclic phosphenium (NHP+) ligands and NHP-containing transition metal complexes ........................................................................................................ 1 1.1 Introduction to N-heterocyclic phosphenium cations ................................................................ 2 1.2 History ............................................................................................................................................................. 2 1.3 Synthetic routes to NHP+s ....................................................................................................................... 5 1.4 NHP-metal coordination compounds ................................................................................................. 7 1.5 Binding modes .............................................................................................................................................. 9 1.6 Scope of this thesis ..................................................................................................................................... 17 1.7 References ...................................................................................................................................................... 20 Chapter 2. Coordination of N-heterocyclic phosphine- and phosphenium-containing pincer ligands to first-row transition metals: Evidence for reactive electrophilic metal- phosphenium intermediates ........................................................................................................................................ 22 2.1 Introduction .................................................................................................................................................. 23 2.2 Results and discussion .............................................................................................................................. 24 2.2.1 Coordination of [PP(Cl)P] to CoCl2 .................................................................................... 24 2.2.2 Addition of [PP(X)P] ligands (X = Cl and I) to copper(I) halides .......................... 29 2.2.3 THF-ring opening and insertion into P-I bonds .......................................................... 32 2.2.4 Aryl group transfer to the electrophilic phosphorus ................................................ 36 2.2.5 Dimerization and halide migration ................................................................................... 41 2.2.6 Computational investigation of complex 11 intermediates via DFT .................. 45 vi 2.3 Conclusion ...................................................................................................................................................... 50 2.4 Experimental ................................................................................................................................................. 51 2.4.1 General information ................................................................................................................ 51 2.4.2 X-ray crystallography procedures ..................................................................................... 52 2.4.3 Computational details ............................................................................................................. 53 2.4.4 Synthesis of [PP(Cl)P]CoCl2 (1) .......................................................................................... 53 2.4.5 Synthesis of [PP(F)P]CoCl2 (2) ........................................................................................... 54 2.4.6